A Year of Nuclear Fleet Slowdowns
This chart shows weekly average reported power across active U.S. nuclear reactor units during the NRC’s trailing-year status file. The fall and spring slowdowns are visible in this one-year window, which cannot establish that the pattern recurs across years.
The fall low, 79.3% in the week of 2025-10-13, was also the lowest week in the file; the spring low was 79.5% in the week of 2026-04-20.
What does it show?
The NRC’s one-year status file contains a fall trough of 79.3% and a spring trough of 79.5%. One year cannot tell us whether that pattern recurs.
Methodology
Parse the NRC Power Reactor Status Report for the last 365 days. Exclude units that never reported positive power anywhere in the trailing-year file, then average each remaining reactor’s daily reported power percentage within ISO weeks. Days on which fewer than 90% of the file’s median reporting-unit count appear are omitted, as are weeks with fewer than three reporting days. A fall or spring trough is reported only when its weekly low is at least five percentage points below the trailing-year weekly median. Limitations: Reported power is an operating-status percentage, not metered generation. The fleet average weights reactor units equally rather than by nameplate capacity. Zero power can reflect planned refueling, maintenance, or unplanned outages; this file does not assign a cause. The source contains only a trailing year, so it cannot establish whether the seasonal pattern is typical across years.